This invention concerns a mold for a continuous casting system having a shaping mold body made of a material that has a high level of thermal conductivity, such as copper or a copper alloy.
Molds are used for establishing the profiles of solids that are manufactured in a continuous casting process. The mold is one of the most important components of a continuous casting system, as the melt begins solidifying while within it.
The mold design, in general, includes an outer steel construction. The actual shaping component of the mold is the mold body. Mold bodies are today made almost exclusively of copper or a copper alloy. The function of the steel jacket is to position the mold body and to provide the water circulation required for cooling.
In order to protect it against wear, the mold body is typically provided with an internal plating made of a wear-resistant material such as nickel or chromium. An example of such a continuous casting mold with wear-resistant coating is described in German Patent No. 31 42 196 C2. The friction characteristics and therefore the service life of the mold body can be improved in this manner.
As liquid steel cools while flowing through the mold body, it solidifies in the outer areas, forming a billet layer with a continuously growing thickness. The cross-sectional geometry of the billet changes by shrinking.
Thus, in addition to shaping the billet, the mold body also has the important function of ensuring the formation of a sufficiently thick, high-strength and defect-free billet layer through the continuous removal of heat.
Excessive heat removal and cooling of the steel melt at the beginning of the solidification process, particularly in the meniscus area, negatively affects the billet surface quality. It may result in microcracks in the surface and microstructure defects. These are formed mainly near the edges of the mold body. Furthermore, there is a danger of the billet becoming seized in the tapering mold body.
In order to reduce heat removal in the meniscus area, the method of electromagnetically agitating the melt in the mold body is known. This method is, however, relatively expensive. Furthermore, attempts have been made to reduce heat removal using vertical slots in the internal wall of the mold body or inserts made of refractory material.
Tests with thicker internal wear-protection platings have also been conducted. Due to the difference in heat elongation coefficients of the mold body (mainly copper) and the wear-resistant plating (mainly nickel), considerable stresses appear in the wear-resistant plating. Adherence is negatively affected and cracks may form.
There remains a need to provide a mold body where heat removal, particularly in the meniscus area, is reduced and better billet quality is achieved.